Field emission apparatuses that are currently being used, such as a field emission type backlight, a field emission flat lamp (FEFL), a field emission display, and the like, employ a sharp cold cathode as means for emitting accelerated electrons for exciting phosphors, instead of a thermal cathode used in a conventional cathode ray tube. In other words, electrons are emitted through tunneling effect of a quantum mechanics by concentrating a high electric field on the emitter constituting the cold cathode. U.S. Pat. No. 3,970,887 issued to Donald O. Smith, et al. discloses a structure in which a silicon (Si) micro tip is formed in a semiconductor substrate and an electric field is applied to the tip through a gate electrode, thus emitting electrons. This kind of a field emission apparatus is problematic in that it requires a very high gate voltage for electron emission since the work function of a material used in the micro tip is great, and in that the micro tip is easily damaged.
Thus, a diamond film has recently been in the spotlight as the emitter. In recent years, active research has been done on carbon nanotube (CNT) that radiates electrons even in an electric field, which is about 1/10 lower than an electric field for electron emission of the diamond film.
No matter which emitter is used, it can be used practically only when a wide light-emitting area, high brightness, a longer lifespan, and a simplified process are accomplished.
An existing field emission apparatus includes a two-pole or three-pole structure. In the two-pole structure, a method of extracting electrons from a field emission material by applying a high voltage between an anode electrode and a cathode electrode and exciting phosphors with the electrons to emit light is used. The two-pole structure is advantageous in that it demands a low manufacturing cost; it is easy to manufacture them; and a wide light-emitting area can be easily fabricated, but is problematic in that it demands a high driving voltage; and it has low brightness, which can be generated stably, and low emission efficiency.
Korean Patent Laid-Open Publication No. 2000-74609, U.S. Pat. No. 5,773,834, Korean Patent Laid-Open Publication No. 2001-84384, and Korean Patent Laid-Open Publication No. 2004-44101 disclose the field emission apparatuses of the three-pole structure. In the three-pole structure, an auxiliary electrode, called a gate electrode, is spaced apart from a cathode electrode by several tens of nanometers (nm) to several millimeters (mm) in order to easily extract electrons from a field emission material. Phosphors on the anode electrode side are excited with the extracted electrons by applying a high voltage between the anode electrode and the cathode electrode, so that light is emitted. This three-pole structure can lower a driving voltage significantly and generate a high brightness, but has been problematic in that the manufacturing cost is relatively high, manufacturing time is taken long, and a light-emitting area is small.
A lateral gate type field emission apparatus disclosed in Korean Patent Laid-Open Publication No. 2004-44101 is shown in FIG. 1. Referring to FIG. 1, cathode electrodes 10 are formed on a surface of a rear substrate 5. An emitter 20 comprised of carbon nanotube is formed on the cathode electrode 10. A gate electrode 25 is spaced apart from the cathode electrode 10 at a predetermined interval, and is adjacent to the rear substrate 5 by the mediation of an insulating layer 15. A phosphor layer 30, an anode electrode 35 formed of an indium tin oxide (ITO), a front substrate 40 and so on are disposed opposite to the rear substrate 5.
In the conventional field emission apparatus of three-pole structure including the lateral gate type, brightness irregularity occurs since electrons are not radiated from the gate electrode 25 and heavy load is given to the emitter 20 since electrons are radiated only from the emitter 20 formed on the cathode electrode 10. Accordingly, there are problems in that a lifespan is short and brightness is low.
Korean Patent Application No. 2004-70871, which was previously filed by the applicant of the present invention in order to solve the conventional problems, is advantageous in that it can improve brightness and save the manufacturing cost, but does not accomplish the advantages of a ground driving method according to the present invention in a method of driving a field emission apparatus having a dual emitter.